The fields of forensics, paternity testing, tissue typing, and personalized medicine routinely use DNA-based techniques for identity determinations, genotyping, phenotypic prediction, and in the prediction and/or prevention of disease. DNA typing involves the analysis of alleles of genomic DNA with characteristics of interest, commonly referred to as “markers.” Most typing methods in use today are specifically designed to detect and analyze differences in the length and/or sequence of one or more regions of DNA markers known to appear in at least two different forms in a population. Such length and/or sequence variation is referred to as “polymorphism.” Any region (i.e., “locus”) of DNA in which such a variation occurs is referred to as a “polymorphic locus.”
In recent years, the discovery and development of polymorphic short tandem repeats (STRs) as genetic markers has played an important role in DNA typing. STRs have become the primary means for human identity and forensic DNA testing. The Combined DNA Index System (CODIS) DNA database operated by the Federal Bureau of Investigation stores the DNA profile information of selected individuals. The CODIS profile includes 13 STR markers (13 loci with STR repeats), two additional allelic markers and AMEL, a sex determination allele. The selected DNA profiles can be from many possible sources, e.g., convicted offenders, arrestees, missing or unidentified persons, and missing persons reference DNA (blood relative). Comparison of the DNA profile of an unidentified sample to CODIS DNA profiles has provided potential identification matches or investigative leads of possible perpetrators.
Matching and comparing DNA profiles produced from existing commercial STR assays provides continuity and comparability of the DNA profiles within and between databases and improved STR assays. The use of a size standard, i.e., an allelic ladder, composed of amplified alleles from a locus, permits comparison of STR alleles for the locus between databases, STR assays, laboratories and samples to increase the power of the DNA profiling system.
Thus, identification of rare alleles, which can be highly discriminating, further improves determination of alleles in unidentified samples. Therefore, there exists a need in the art, to improve DNA-based technologies based on the discovery of new STR alleles in human DNA sequences.